Phosphorylation of the translation initiation factor eIF-2alpha has been shown to be a major mechanism controlling protein synthesis in eukaryotic cells, yet the developmental and physiological consequences of this regulation are largely unknown in whole organisms. By using the diverse tools of Drosophila genetics we propose to critically test the functional importance of eIF-2alpha phosphorylation and, in addition, investigate the function of an eIF-2alpha kinase, GCN2. In lower eukaryotes, GCN2 senses amino acid deprivation and through the general control pathway derepresses amino acid biosynthesic genes. In higher eukaryotes the function of GCN2 is unknown but likely to be more complex by virtue of its expression in the developing and mature central nervous system and because the response to amino acid deprivation in higher eukaryotes is dependent upon whether essential or non- essential amino acids are limiting. The most important objective of this proposal is the isolation of loss of function mutations of eIF-2alpha and GCN2. Loss of function mutations are likely to give us immediate clues as to developmental functions and these mutations will be form the basis of several of the other specific aims. Other experiments are proposed to identify downstream targets of GCN2 and specific developmental and physiological processes impacted by the control of translation initiation as mediated by the phosphorylation of eIF-2alpha.